crankshaft/pg/doc/03_overlap_sum.md

Aereal Weighting

Aereal weighting is a simple interpolation technique to assign a value to a polygon given a set of polygons with one value assigned to each one.

The value is assigned by averaging the values of intersecting areas weighted by the intersection area.

Its accuracy depends on the values assigned to reference areas being homogeneous over each area.

The cdb_overlap_function takes three required parameters:

• geometry a Polygon geometry which defines the area where a value will be estimated.
• table_name: name of the values table that provides the source values; this table must have a geometric column the_geom containing the polygons to which values are assigned.
• column_name: name of the column that contains the values in the values table (should be a numeric column)

There's also an additional optional parameter to define the schema to which the values table belongs. This is necessary only if it is not in the search_path. Note that table_name should never include the schema in it.

• schema_name name of the schema that contains the values table

This function returns a numeric value resulting from the aggregation of the polygons in